1. Field of the Invention
The invention is in the general area of touchpads and touch sensors for handheld computerized devices.
2. Description of the Related Art
Handheld computerized devices (i.e. handheld devices equipped with microprocessors and bit-mapped displays, often touch sensitive displays) such as cell phones, personal digital assistants (PDA), game devices, tablet PCs (such as iPad), etc., are playing a more and more important role in everyday life, and are becoming more and more indispensible. With the advance of technology, and improvements in the handheld computerized devices' processing power, both function, and memory space is increasing at an amazing pace. Meanwhile the size of the handheld computerized devices continues to get smaller and smaller.
To meet this challenge, the designers of handheld computerized devices typically use two approaches. One approach is to make the keyboard keys smaller and smaller, miniaturizing the keys. Additionally the keyboard keys may be given multiple functions—i.e. overloaded, and more complex function keyboard keys may be introduced as well.
The other approach is to make the display a touch sensitive display, and use touch screen keyboards, or so called “soft keys”. Here a user may use a stylus pen or finger to select the soft keys through a graphical user interface. Due to the optical illusions introduced by the display screen, however, the soft keys cannot be too small, because otherwise a single finger press will activate multiple keys. As a result, the designer may have to divide the keys into different groups and hierarchies, and only display a small number of keys on the screen.
Both current approaches have some severe drawbacks: the user input area can occupy a significant portion of the front panel, and the user input process, although requiring a large amount of user attention to operate, still is very error prone.
Often a user has to use one hand to hold the handheld computerized device, and use the other hand to input data, thus occupying both hands. A user will often have to go through a long sequence of key strokes, and switch back and forth among different user interface screens, in order to complete a fairly simple input. As a result, there is a significant learning curve for a user to learn the overloaded keys, function keys, key grouping, and key hierarchies in order to operate the handheld computerized devices efficiently.
To simplify the user interface, various alternative methods employing touch sensors, touchpads, touch screens and the like (also called touch sensitive input devices and trackpads) have been proposed.
Yoon et. al., in U.S. patent application Ser. No. 12/691,892, proposed a mobile terminal having a dual touch screen and method of controlling content therein. This patent application disclosed a handheld computerized device with two built-in touch sensors, one located on the device's front touch screen, and a second touchpad sensor located on the rear of the device.
Cholewin et. al. in U.S. patent application Ser. No. 12/505,755, as well as Gorsica et. al. in U.S. patent application Ser. No. 12/492,369, proposed various types of portable handheld computerized devices with either opposing built-in touch sensitive surfaces, or alternatively constructing handheld computerized devices with the touchpad on the rear surface.
Luo, in U.S. provisional patent application 61/327,102, and U.S. non-provisional patent application Ser. No. 12/773,075, both of which are incorporated herein by reference, introduced a method that utilized a back mounted touchpad. This method took touch input data from this back mounted touchpad, and used software models of the hand to in turn generate a virtual image of the most likely user rear hand position, often superimposed upon a virtual keyboard layout. The net effect was to attempt to make the handheld computerized device “transparent”, thus allowing the user to visualize the most likely position of his hands and fingers that were otherwise hidden because they were behind the device. Thus the method allowed the user to use a touchpad keypad on the back of the device to input keystrokes and mouse actions, and this touchpad data was reflected on the display screen on the front of the handheld computerized device as “virtual fingers” or equivalent.